Methods for decoration of the surface of plastic or metal parts include, for example, a direct printing process and a decalcomania process. However, the direct printing process has a problem of being unsuitable for molded products having a complex shape, whereas the decalcomania process has a problem of being costly. In the meantime, there are methods for decoration of the surface of plastic or metal products at low costs: for example, a film insert molding process in which a base resin is injection molded while a film of acrylic resin etc. having been shaped by vacuum forming in advance is inserted into a cavity of an injection molding die; and a film in-mold molding process in which a base resin is injection molded while a film having not been shaped is inserted into a cavity of an injection molding die. And there have been proposed various methods for producing acrylic films suitable for this application. For example, there are known a method in which the reduced viscosity of plastic polymer, the particle size of rubber-containing polymer, the rubber content etc. are specified (Japanese Patent Laid-Open No. 8-323934) and a method in which the reduced viscosity of acrylic polymer and the content of multi-layer structure acrylic polymer are specified (Japanese Patent Laid-Open Nos. 10-279766 and 10-306192). The films produced by these methods are known to excel in surface hardness, transparency and moldability. However, these patent specifications do not describe the problem of stress-whitening occurring in the films or cracks occurring at the time of film cutting.
For the problem of stress-whitening occurring in films, Japanese Patent Laid-Open No. 2002-80678 states that the problem can be solved by specifying the particle size of rubber-like polymer used to be less than 2000 Å. In this document, vacuum forming is performed at pre-heating temperatures as relatively high as 125 to 145° C.; however, some of the films described in the document undergoes stress-whitening at pre-heating temperature of 125° C. or 130° C. Stress-whitening is more likely to occur at lower heating temperatures, and even by the method described in this document, a film is hard to form by vacuum forming at temperatures lower than the above described temperatures. This document does not mention at all the problem of cracks occurring in a film when cutting the molding flash at the end portion of the film at finishing step. Specifically, in any one of these films, when laminating the film on a molded product of a complex shape at low temperatures, stress is concentrated in the corner of the film, and the film is likely to undergo whitening, resulting in significant deterioration of its value as a product. These films also have a problem of cracks caused when cutting at a finishing step the molding flash at the end portion of the film laminates obtained by a film insert molding process or film in-mold molding process.
Under these circumstances, the present inventors directed tremendous research efforts toward the development of a film in which stress-whitening hardly occur even by molding at low temperatures and cracks hardly occur at the time of cutting of the film. And they have found that a film, composed of a resin composition that includes a multi-layer structure acrylic polymer using a special acrylic ester rubber-like polymer and a methacrylic polymer, undergoes less stress-whitening even by molding at low temperatures and has high surface hardness, excellent transparency, also excellent transparency even after heating and excellent weatherability, and its elongation at the time of tensile breakage is high and its moldability, surface properties and processability (cracks are less likely to occur at the time of film cutting) are all excellent.